2011-01-14

Opportunity Sol 702 (Spirit Sol 723)

Because Monday is MLK Day, we're doing a 3-sol plan this weekend. We expect it to be fairly simple, if a little scary: we're putting Opportunity's IDD in its new stowed configuration today. This is the "Rodin's Thinker" pose: the IDD will be swung up over the solar panels, elbow-out, with the turret resting about 5cm over the left front solar array hinge. Ashitey's worked everything out in the testbed, where they've even tried driving in this configuration. But it's scary all the same.

Actually, just putting the IDD in that pose won't be scary -- driving like that will be.

Anyway, our day will be relatively simple. Unlike Spirit's. Spirit has turned around to IDD the chewed-up Paso-Robles-like stuff she turned up while climbing Husband Hill. This stuff appears to be salts, and since salts are mobilized by water -- you know, the stuff we're here to find evidence for -- most of the science team is hopping-up-and-down excited about it. (Though not Larry Soderblom, who dismissed it in email as "bright dirt." He thinks we should spend this time zooming toward Home Plate, as we're increasingly behind schedule. I can't say I think he's wrong, but I'm no scientist.) And they're doing one hell of an IDD campaign, some twelve targets or so over the 3-day weekend.

John Wright's the RP-1, so I have no doubt it'll get done, and get done well, too. But people keep asking me, "Aren't you glad you're not on Spirit?" And I have to tell them no. Truth is, I wish I were John. The harder the task, the greater the glory.

I guess I'll have to let him have a little glory.

Since we have a lot of time, I go ahead and get to work on next week's drive. I expect a lot of scrutiny, so the earlier I get a handle on this, the better. Happily, Ken Herkenhoff is out here, so I discuss the bump target with him and Wendy Calvin. They want us to get to a pair of rocks -- "Upper Overgaard" and "Lower Overgaard" -- that are slightly ahead of us and to the right. Before going there, we need to back up 1m and image the outcrop we've been parked in front of since the IDD anomaly.

Normally, this would be trivial: turn on visodom, back up, take our pictures, turn, and bump forward to the new target. But, oh, the restrictions we labor under now! In addition to the limitations we already have when driving Opportunity -- the requirements for periodic slip checks and the problems induced by the failed RF steering actuator -- we have new restrictions caused by the IDD's new stow configuration. In particular, we've decided we can't tolerate a drop of more than 3cm, as this might cause the arm to jounce too much and whack the turret against the solar panel. So we can't drive over anything bigger than two or three centimeters -- in common units, about an inch.

You think there will be anything bigger than that between us and Victoria Crater, still some kilometers away across Meridiani Planum? Naaahh ....

And, of course, since we're also restricting the IDD's azimuth -- to ensure that we can still drive even if it fails altogether -- we have to really nail the drive.

And there are a couple of obstacles of just the right size, right where we need to go. Of course. (And there is no position that gets both Upper Overgaard and Lower Overgaard into the new, sharply narrowed work volume, without doing something like driving way around and approaching from a different direction. Which we won't.)

So I have to plan the drive very, very carefully, and one crazy thing I come up with is not to use visodom. This is something of a gamble, but I think it's a sound one. Our slip is likely to be low, and it will carry us mostly away from the many 3cm-or-larger "obstacles" scattered all around us. It might mean we need an additional sol for fine positioning, but I can sell that. Everyone's so happy to be moving at all, they'll buy it. The alternative is to risk a bad visodom position update that would cause the rover to drive farther than it's supposed to, climbing the obstacles and possibly forever damaging the arm.

Did I say I wanted this to be hard, to increase the consequent glory? I take it back. Less glory, please.

Just as we're wrapping up for the sol, about 7 PM, we get the downlink from yestersol. I take one look and sigh. "Bad news, everyone!" I announce. "The last sequence faulted out near the end, during the return to the ready position." I hope this is another joint-1 stall, as opposed to a completely different problem, but that data hasn't come down yet. "So the stow sequence we built today won't execute over the weekend. Worse, the MB is aimed directly into one of the HAZCAMs." This is a condition we're supposed to avoid; the instrument's radiation source can damage the cameras.

So should we try to recover? Luckily for us, Jake Matijevic is still here. Jake gives us a pass on the MB situation, pointing out that the MB's radiation source has degraded significantly since we got to Mars, and at its current distance from the cameras, it should no longer be a threat to leave it like this for a few days. Emily decides not to reassemble the team at this point to try to fix the problem, especially because, due to missing data in the pass, we don't even know exactly what the problem is yet.

So we go home. I can't help thinking that one consequence of this fault is that it'll be at least one more sol before we can stow, so at the earliest we'll drive Wednesday instead of Tuesday (the day after the holiday). Depending on the analysis, we might have to push the drive later than that. And since I'm on Opportunity only Tuesday and Wednesday of next week, that means I might not get to do the first Mars drive in the new stowed configuration.